In recent years, there has been a growing trend to incorporate advanced various functions into electronic devices, such as mobile phones and car navigation systems. In such a trend, a touch panel has been widely employed for an input device of various electronic devices. For example, a light-transmissive touch panel is attached on the front surface of a liquid crystal display (LCD) element. A user presses a touch panel with a finger or stylus, while viewing letters, symbols and graphics shown by the LCD element on the back surface of the touch panel and selects a desired function. As the demand for a touch panel increases, manufacturers have sought a user-friendly touch panel with good visibility.
An input device employing a conventional touch panel will be described with reference to FIG. 5.
FIG. 5 is a sectional view of a conventional input device. For sake of clarity, the figure shows dimensions enlarged in the thickness direction.
The input device shown in FIG. 5 has LCD element 8 on which polarizing plate 7 is disposed, and touch panel 6. Touch panel 6 has upper substrate 1, lower substrate 2, upper conductive layer 3 and lower conductive layer 4. Substrates 1 and 2 are made of a light-transmissive film. Conductive layers 3 and 4 are also formed of light-transmissive material, such as indium-tin oxide. Upper conductive layer 3 is disposed on the bottom surface of upper substrate 1, and lower conductive layer 4 is disposed on the top surface of lower substrate 2. Conductive layers 3 and 4 are sandwiched between upper substrate 1 and lower substrate 2.
A plurality of dot spacers (not shown) are formed with insulating resin at predetermined spaced intervals on the top surface of lower conductive layer 4. A pair of upper electrodes (not shown) is formed at both ends of upper conductive layer 3; similarly, at both ends of lower conductive layer 4, a pair of lower electrodes (not shown) is formed in an arrangement perpendicular to the upper electrodes.
Frame-shaped spacer 5 is disposed between upper conductive layer 3 and lower conductive layer 4 to separate them. Spacer 5 has an adhesive layer (not shown) coat-formed on the top and bottom surfaces or either one of the surfaces, by which the peripheries of upper substrate 1 and lower substrate 2 are bonded with each other. Upper conductive 3 faces lower conductive layer 4 at predetermined spaced intervals.
Such structured touch panel 6 is disposed on LCD element 8 through polarizing plate 7 and mounted on an electronic device. Each pair of upper electrodes and lower electrodes is connected, via a connector and a lead wire (not shown), to the electronic circuit (not shown) of the electronic device. Now will be described how such structured touch panel works. A user presses the top surface of upper substrate 1 with a finger or stylus, while viewing the displays shown by LCD element 8 on the back surface of touch panel 6. The application of depressing force depresses down upper substrate 1, allowing a position of upper conductive layer 3 corresponding to the depressed position to make contact with lower conductive layer 4. Through the connection of the conductive layers, voltage is applied to the upper electrodes and the lower electrodes from the electric circuit. The electronic circuit detects the depressed position from voltage ratio between the electrodes. The electronic device thus recognizes the user's selection and switches to the desired function.
In the operation above, lamplight 9 illuminates the displays, such as letters, symbols and graphics, shown by LCD element 8. Here, suppose that polarizing plate 7 disposed on LCD element 8 absorbs Y-directional light wave perpendicular to X-directional light wave. In this case, the lamplight 9 changes to X-directional linearly polarized lamplight 9a and exits as X-directional linearly polarized output light 9b from the top surface of substrate 1.
Suppose that a user puts on smoked sunglasses for blocking reflected light and operates the touch panel in direct sunlight. In this case, although the visibility is lowered, the user can recognize the displays of LCD element 8. However, if the sunglasses are polarized sunglasses that absorb X-directional polarized light wave, the user cannot recognize the displays of LCD element 8 illuminated by X-directional linearly polarized output light 9b. This can cause a problematic situation when the user operates the touch panel in the driver's seat under the glares of sunlight in midsummer.
For example, Japanese Patent Unexamined Publication No. 2006-107015 is known in a prior-art reference relating to the present invention.
According to the conventional input device, as described above, when the user operates touch panel 6 with the use of polarized sunglasses, a problem arises; if the polarized sunglasses absorb light wave having a direction the same as the direction in which lamplight 9 is polarized by polarizing plate 7, the user cannot recognize the displays of LCD element 8.